This invention relates generally to fluid dispensing systems, and more particularly to a system and method for dispensing a predetermined volume of fluid. Even more particularly, this invention relates to a system and method for accurately blending two or more fluids.
Onsite chemical mixing and delivery is difficult in industries requiring precise dilution and mixing ratios. Deterred by the difficulties involved in producing their own chemistry, such as labor expenses and precise molarity tolerances, industries such as semi-conductor fabrication typically purchase pre-diluted and/or pre-mixed chemicals. These pre-mixed chemicals, supplied by outside companies, vary slightly in price depending on concentration. The price per barrel of a chemical concentrate is typically only slightly higher than that of a dilution of the same chemical. Further, the freight cost of delivering multiple drums of chemicals is substantial.
Some industries opt to produce their own chemistry, but at the cost of large mixing vessels that are not typically automated. These large mixing vessels are useful only to entities able to afford the system""s maintenance costs as well as supply the space needed to house such a system.
Notwithstanding these limitations, onsite mixing and delivery systems provide many advantages over purchasing pre-mixed chemicals. By utilizing a chemical delivery and mixing system, a single barrel of concentrate chemical produces many times its volume in diluted solution, depending on the desired concentration of the dilute. Thus, a single barrel of concentrate, used to produce many barrels of dilute via a chemical delivery and mixing system, greatly reduces freight costs associated with chemical delivery. In addition, onsite dilution and mixing increases the variety of chemical concentrations and mixtures that are immediately available, without requiring a corresponding increase in the number of chemicals that must be purchased from chemical manufacturers, thereby providing the logistical and administrative advantage of reduced inventory.
What is needed is a compact system capable of mixing, blending, and delivering precise volumes of chemicals onsite, allowing small industry to manufacture chemistry in desired molarities or weight ratios at minimal cost, and in reduced batch sizes.
The present invention provides an advantage over the prior art by providing a compact fluid delivery system capable of producing large or small quantities of precisely mixed chemicals on demand. The embodiments of the invention shown herein are automated, but the present invention can be implemented in a manual or semi-manual system while retaining many of the advantages of the invention.
Fluid delivery systems according to the present invention include one or more measure modules for measuring and delivering precise volumes of fluids. Each measure module includes a fluid inlet port, a vessel, an overflow aperture, and a fluid outlet port. The vessel receives fluid via the fluid inlet port. The overflow aperture is positioned to define a predetermined retention capacity of the vessel, allowing excess fluid to flow out of the vessel while retaining the predetermined volume in the vessel. The measure module measures fluid by filling the vessel beyond its retention capacity, and then allowing the excess fluid to flow out through the overflow aperture.
An optional calibrating device (e.g., calibrating rod, slugs, inflatable bladder, etc.) facilitates fine adjustment of the retention capacity of the vessel. Alternatively, the position of the overflow aperture is adjustable. For example, in one embodiment the aperture is disposed atop a vertical drain tube, such that the height of the drain tube defines the retention capacity of the vessel.
An optional overflow reservoir collects the excess fluid flowing out of the vessel. The overflow fluid is transferred back into the vessel at the beginning of the next fill cycle. Use of the overflow reservoir prevents waste of expensive chemicals, and reduces the cost associated with disposal of hazardous chemicals.
One particular embodiment of the invention is capable of operation in two modes. In the first mode, the measure module operates as described above. In a second mode, however, the vertical drain tube functions as the xe2x80x9cvesselxe2x80x9d by measuring the amount of fluid to be dispensed. Excess fluid flowing out of the drain tube is collected by the vessel, which functions in the second mode as the xe2x80x9coverflow reservoir.xe2x80x9d
Various fluid delivery systems are constructed by interconnecting a plurality of the above-described measure modules in different ways. For example, in one embodiment a plurality of chemicals are blended by coupling the outputs of a like plurality of measure modules. Each of the measure modules measures and dispenses a particular one of the constituent chemicals of the mixture. The relative concentration of each chemical in the mixture depends on the retention capacity of the vessel of the measure module associated with that chemical. In another embodiment, the output ports of two measure modules are coupled together to dilute a chemical concentrate with water. The diluted mixture is provided to other measure module pairs for further dilution, such that the system is able to provide several different dilutions (e.g., 10:1, 50:1, 100:1, etc.) of the concentrated chemical.
In the particular embodiments shown, the fluids discharged from the measure modules are blended in a fluid mixing line. To facilitate even more uniform mixing, flow controllers are interposed between the fluid output ports of the measure modules and the fluid mixing line, so that the fluids are introduced into the fluid mixing line at a rate proportional to their relative concentration in the mixture.